This invention relates to a method for fixing ions in porous media and is particularly directed towards the fixation of radioactive ions in soil. Although every precaution is taken to avoid release of radioactivity to the environment, it is not inconceivable that soil could be contaminated with radioactive material as a result of a leak, spill, or other accidental release. In such an event, it will be necessary to localize the contamination as much as possible and to prevent any spreading of the radioactive contamination. Radioactive contamination of soil is of grave concern as radioactive ions could be leached and migrate through the soil, eventually entering water supplies for surrounding areas. Strontium and cesium are of particular concern because of the very long half-lives of their radioactive isotopes and because of the manner in which they concentrate in certain body tissues. It is therefore essential to find techniques which ensure that the radioactive ions will remain isolated from the environment for long periods of time. While radioactive contamination can be removed for safe storage elsewhere by excavating the soil around the spill, the excavating operation itself could cause a further spreading of the contamination. Therefore, fixation of the radioactive contamination of the soil in situ is preferable to excavation. Techniques are available for immobilizing radioactive contamination of soil in situ such as by scavenging the contaminated soil by spraying the surface with a polyurethane foam which picks up contamination, soil, and rocks and forms a protective coating over the contaminated area, thereby preventing further spreading of the contamination from weathering. Another technique, disclosed by one of the present applicants in U.S. Pat. No. 3,723,338, provides for injecting into the contaminated soil a polymerizable monomer which polymerizes around the particles of the soil, immobilizing the radioactive material by physical entrapment. Unfortunately, these prior art techniques do not prove completely satisfactory in preventing the spread of leachable radioactive ions, strontium-90 and cesium-137 in particular. These ions can be leached and gradually migrate from the polymerized mass into the surrounding free soil. The present invention is an improved method for fixing such radioactive ions in the soil.